docs: def Gregory_Scott(x, rhol, rhog):
      r'''Calculates void fraction in two-phase flow according to the model of 
      [1]_ as given in [2]_ and [3]_.
      
      .. math::
          \alpha = \frac{x}{\rho_g}\left[C_0\left(\frac{x}{\rho_g} + \frac{1-x}
          {\rho_l}\right) +\frac{v_{gm}}{G} \right]^{-1}
          
      .. math::
          v_{gm} = 0
  
      .. math::
          C_0 = 1.19
          
      Parameters
      ----------
      x : float
          Quality at the specific tube interval []
      rhol : float
          Density of the liquid [kg/m^3]
      rhog : float
          Density of the gas [kg/m^3]
  
      Returns
      -------
      alpha : float
          Void fraction (area of gas / total area of channel), [-]
  
      Notes
      -----
          
      Examples
      --------
      >>> Gregory_Scott(0.4, 800., 2.5)
      0.8364154370924108
  
      References
      ----------
      .. [1] Gregory, G. A., and D. S. Scott. "Correlation of Liquid Slug 
         Velocity and Frequency in Horizontal Cocurrent Gas-Liquid Slug Flow." 
         AIChE Journal 15, no. 6 (November 1, 1969): 933-35. 
         doi:10.1002/aic.690150623.
      .. [2] Xu, Yu, and Xiande Fang. "Correlations of Void Fraction for Two-
         Phase Refrigerant Flow in Pipes." Applied Thermal Engineering 64, no. 
         1-2 (March 2014): 242–51. doi:10.1016/j.applthermaleng.2013.12.032. 
      .. [3] Woldesemayat, Melkamu A., and Afshin J. Ghajar. "Comparison of Void 
         Fraction Correlations for Different Flow Patterns in Horizontal and 
         Upward Inclined Pipes." International Journal of Multiphase Flow 33, 
         no. 4 (April 2007): 347-370. doi:10.1016/j.ijmultiphaseflow.2006.09.004.
      '''
      C0 = 1.19
      return x/rhog*(C0*(x/rhog + (1-x)/rhol))**-1